The present invention relates to an actuator, and more particularly to an actuator that can produce an optimum torque output within a given weight and size envelope, and transmit the torque to a rotating shaft without lost motion or backlash.
It is conventional in the use of rotationally actuated valves, such as rotary plug valves and butterfly valves, to employ an actuator that resolves a linear actuator translation into a rotational moment. This rotational force is utilized to open and close a valve gate or valve plug. An example rotary valve is shown and described in U.S. Pat. No. 6,076,799 to Baumann (Baumann ""799). In Baumann ""799, a linkage is provided at the end of a rotary valve shaft. The linkage inter-connects with a linear actuating device. Such actuators often include large mechanical housings that receive air and execute translation of the linear actuator component by interaction with a rolled diaphragm that moves in response to applied pressure. The housing is supported relative to the valve casing by a large framework that provides room for the linkages to operate internally.
The above-mentioned valve actuator requires a relatively large amount of space around the actual valve casing for the actuator mechanism. In some instances, it is desirable to have a smaller actuator mechanism that is simplified, relatively light weight, efficient, can be disassembled with ease and without causing a safety hazard, and is reversible with disassembly or additional parts.
Furthermore, it is known that actuator linkages that resolve linear transaction into rotational movement are often prone to backlash and/or may be difficult to assemble onto a shaft. A conventional approach is for rotary valve shafts to have a square cross section to provide edges for an actuator to grab on to for translation of rotary motion. However, square cross sections have a tendency to create backlash if the linkage is not accurately sized to the shaft. If the square cross section is disposed in a linkage that is not relatively close in size, the square shaft may begin to rotate within the linkage, causing backslash and eventually excessive wear. Some solutions make use of set screws or complicated clamps to increase the strength of the coupling between the linkage and the shaft. However, these structures add to the complexity of the interconnection between components, and therefore increase cost and assembly time for valves using such actuators.
There is a need for a rotary pneumatic actuator that can translate linear movement into rotational movement without loss of motion, or backlash. The actuator must also be relatively lightweight, simple in construction and use, efficient in the transmission of torque, and be reversible in direction of rotation without disassembly or additional parts. The present invention is directed towards further solutions to address these needs.
In accordance with one example embodiment of the present invention, a rotary actuator assembly includes a housing having a central bore with a first end and a second end. A piston is disposed within the housing and is linearly movable along an axis of the central bore. A rolling diaphragm is disposed within the housing and coupled with the piston. A bifurcated linkage having an end flange couples with the piston and the rolling diaphragm. An articulatable coupling further connects the bifurcated linkage with a rotating linkage. A spring button, which can be cone shaped, is disposed within the housing. A compression spring is retained between the end flange of the bifurcated linkage and the spring button, for example, by a threaded rod and nut. The assembly is arranged such that when force is applied to the rolling diaphragm the bifurcated linkage is linearly transported, which results in the pivoting of the rotating linkage about a pivot point. The pivot point can couple to a valve stem.
The rotary actuator can further include a strip flange coupled with the first end of the central bore and arranged to support the cone shaped spring button. In addition, a cast cup can be disposed at the second of the central bore sealingly engaged with the rolling diaphragm. A lower housing can be provided having a bore offset and perpendicular to the central bore.
In accordance with further aspects of the present invention, a slotted sleeve can be provided that is suitable for receiving a valve shaft. The slotted sleeve is disposed at the pivot point on the rotating linkage distal from the articulatable coupling. The slotted sleeve can have a broached interior.
In accordance with yet another aspect of the present invention, the rotating linkage can be bifurcated, having arms that straddle arms extending from the bifurcated linkage.
In accordance with still another aspect of the present invention, articulatable coupling can take the form of a bushing snapped into a bore and held in place with a riveted pin. In one configuration, arms extended from the bifurcated linkage can elastically deform toward each other, enabling the riveted pin to engage the bushing.
In accordance with still another aspect of the present invention, the actuator can further include a flat flange disposed at the first end of the central bore. There can be a bore disposed within the flat flange. A hand wheel can also be provided having a hollow hub. The hollow hub passes through the bore of the flat flange. The hollow hub, according to one aspect, is slidingly engaged with a nut that is threadingly engaged with a threaded rod and a thrust bearing. The thrust bearing is disposed on the strip flange. Rotation of the hand wheel can rotate the nut about the threaded rod. This action imparts tension on the threaded rod, thereby pulling the threaded rod together with the bifurcated linkage and compressing the compression spring to pivot the rotating linkage about the pivot point. The hollow hub, according to one aspect of the present invention, is formed of a substantially transparent material enabling observation of a position of the threaded rod.
According to further aspects of the present invention, the actuator can include a locking nut suitable for locking the hand wheel to prevent hand wheel rotation. In addition, a position feedback mechanism can be provided that is suitable for indicating a position of the bifurcated linkage within the housing. An inflation cavity can be formed by a cast cup sealingly engaged with the rolling diaphragm. An air passage can be provided between the inflation cavity and a positioning device, the air passage being disposed internal to the housing, thus eliminating the need for heretofore used cumbersome external pipes or tubing.
In accordance with further aspects of the present invention, a method of pneumatically activating a linkage to control a valve includes applying air pressure to an inflatable cavity formed by an end cap and a rolling diaphragm of a central bore in a housing. The inflatable cavity inflates to linearly move a piston and a bifurcated linkage disposed within the housing along an axis of the central bore while compressing a compression spring. The bifurcated linkage is articulatably coupled with a rotating linkage. The rotating linkage pivots in a first direction about a pivot point supporting a valve shaft coupling suitable for controlling rotation of the valve shaft to open or close a valve.
According to one aspect of the present invention, the method can further include deflating the inflatable cavity to recover spring force energy stored in the compression spring and pivot the rotating linkage in a second direction about the pivot point to open or close the valve.
In accordance with yet another aspect of the present invention, a method is provided of actuating a linkage to control a valve. The method begins with rotating a hand wheel in a first direction to rotate a nut that is threadingly engaged with a threaded rod, thereby imparting tension on the threaded rod. The threaded rod pulls together with a bifurcated linkage, linearly transporting the bifurcated linkage and compressing a compression spring. The linear transportation of the bifurcated linkage pivots a rotating linkage about a pivot point supporting a valve shaft coupling suitable for controlling rotation of the valve shaft to open or close the valve.
In accordance with yet another aspect of the present invention, the rotary actuator assembly is provided. The assembly includes a housing having a central bore with a first end and a second end. A bifurcated linkage articulatably couples with a rotating linkage. A rolling diaphragm is disposed within the housing and coupled with the bifurcated linkage. A compression spring is compressible by the bifurcated linkage. The described configuration operates in a manner such that when force is applied to the rolling diaphragm, the bifurcated linkage is linearly transported, which pivots the rotating linkage about a pivot point. A slotted sleeve is provided within the rotating linkage and is capable of receiving valve stems. The slotted sleeve is furthermore able to be elastically formed to tightly grip the valve stems and thereby prevent backlash.